1. Field of the Invention
The subject invention generally relates to a power steering apparatus for turning steerable wheels on a vehicle.
2. Description of the Prior Art
Power steering systems having a rack and a pinion are utilized in nearly all of today's vehicles to steer at least two of the wheels of a vehicle. The steering wheel of the vehicle is typically connected to a pinion gear that is in meshing engagement with a rack. The rack and pinion is supported in a housing and the rack translates the rotational movement of the pinion and steering wheel into a linear movement. The linear movement of the rack is translated to the steerable wheels of the car typically by a tie rod connected to each of the steerable wheels. In addition, power steering systems typically include an assisting force that provides a pressure or a force in proportion to the rotation of the steering wheel for assisting the linear movement of the rack. The assisting force is an additional system that may be a hydraulic system utilizing a hydraulic piston coupled to the rack or electrical system utilizing an electric motor to supply the assisting force to the rack. In either system there is a desire to properly support and allow for adjustments to the meshing engagement between the pinion and the rack during the operational life of the power steering apparatus.
The rack can be supported in the housing by a bearing to reduce the frictional resistance on the linear movement of the rack within the housing. The bearing also supports the rack and typically is adjustable to position the rack in proper meshing engagement with the pinion. The bearing, such as that disclosed in U.S. Pat. No. 6,247,375, utilizes a yoke with a bearing surface that is eccentric to the housing to support and adjust the rack into proper meshing engagement with the pinion. The yoke is installed into a housing of the power steering assembly. Once installed, the yoke is rotated thereby adjusting the support and positioning the rack in proper meshing engagement with the pinion. The yoke is then permanently staked or locked into position with a tool to deform the housing to support and secure the yoke in the rotated position. Since the yoke is staked into position the yoke and bearing support is not adjustable after the complete installation of the yoke into the assembly. Therefore the yoke does not allow for adjustment of the rack after the completed assembly of a vehicle, and further provides no adjustment during the operation of the power steering assembly.
Additional bearing designs such as the bearing disclosed in U.S. Pat. No. 6,435,050, utilizes a two-piece bearing design with a complex assembly involved to support the rack in the housing. The rack bearing is complex with a multiple piece bearing surface and additional bushings are needed to support the rack in proper meshing engagement with the pinion.
The rack and the pinion each include teeth in meshing engagement with each other. The teeth on the rack, the teeth on the pinion, the housing and the bearing wear as a result of continued repetitive use. As these various components wear, the meshing engagement between the rack and the pinion loosens, thereby causing undesirable noise and vibration in the vehicle. Therefore, some rack and pinion steering systems incorporate an adjustment mechanism to continuously adjust the position of the bearing relative to the housing, thereby re-positioning the rack relative to the pinion to compensate for wear on the rack, the pinion, the adjustment mechanism, the housing and the bearing, and provide for a tight meshing engagement between the rack and the pinion. However, the adjustment mechanism may over-tighten the meshing engagement between the rack and the pinion in response to rebound from a severe vibration, impact, load deflection, or when load reversal occurs.